Stable isotopes will be used to label compounds to serve as tracers for diagnostic studies and for evaluation of nutrition and metabolic processes in children. The 13C-triolein test will be evaluated as a diagnostic procedure for fat malabsorption in children and will be compared with 14C-triglyceride breath tests in adults. 13CO2/12CO2 ratios in exhaled breath will be measured by mass spectrometry. Deuterium-labelled glycine cholate will be administered and its kinetics measured in normal infants and in infants and children suspected of abnormal bile acid kinetics. 15N-glycine kinetics will be used to evaluate protein metabolism in children on intravenous hyperalimentation for gastrointestinal diseases. Calcium and magnesium kinetics will be studied in newborn infants. Assay of vitamin D3 metabolites using labelled compounds and mass spectrometry will be evaluated. The feasibility of use of labelled vitamin D3 for kinetic studies will be evaluated in a later phase of the study. Deuterated glucose will be used for kinetic studies in infants of diabetic mothers and in diabetic children. Nuclear magnetic resonance imaging will be investigated for quantitative imaging of the isotopic abundance of labelled compounds in experimental animals. 19F will be used to evaluate bone metabolism and myocardial injury, while 19F-fluorodeoxyglucose will be used to study myocardial and cerebral metabolism in experimental disease states and skeletal muscle metabolism in response to changes in glucose and insulin metabolism. The proposed collaborative investigation brings together current and future research efforts using compounds labelled with stable isotopes at the University of Cincinnati, avoiding needless duplication of equipment and personnel.